Animals can move from place to place, but plants cannot. When an animal is under attack, it can run away or fight back. Plants certainly cannot run away, and they lack teeth and claws. But plants can defend themselves by using both physical and chemical means.
Some plants have their own ways to keep animals away. For example, the leaves of the holly plant have sharp spines(刺) that discourage grass-eating animals. Holly leaves on lower branches have more spines than leaves on upper branches. This is because the lower leaves are easier for most animals to reach.
Some plants , such as the oak trees, have thick and hard leaves that are difficult for animals to eat. Some grasses may contain a sandy material; eating such grasses wears down the animal’s teeth.
Many plants also have chemical defenses. Some plants produce chemicals that taste bitter or cause an unpleasant reaction. Some plants may fight against an attack by increasing the production of these chemicals. When a caterpillar(毛虫)bites a tobacco leaf, the leaf produces a chemical messenger. This messenger sends to the roots the information to produce more nicotine. The higher levels of nicotine discourage the caterpillar.
Many plants depends on both physical and chemical defenses. A certain plant in China , for instance, has prickly(多刺的) leaves, and each prickle contains poisonous venom(毒液). A single experience with this kind of plant will teach an animal to stay away from it in the future.
The holly plant has more spines on the lower leaves because most animals        .

A．can get the lower leaves easily	B．like eating the lower leaves
C．like leaves with sharp spines	D．have teeth and claws

To defend themselves , oak trees use           .

A．chemical means	B．physical means
C．bitter chemicals	D．sandy materials

How does tobacco protect itself against an attack from a caterpillar?

A．Its leaves fight against the attack by physical means.

B．Its roots send a messenger to discourage the caterpillar.

C．Its roots increase the production of nicotine when it is attacked.

D．Its leaves produce poisonous sand to drive the caterpillar away.

What would be the best title for this passage?

A．Plants and Animals	B．How Plants Defend Themselves
C．Attacks and Defenses	D．How Animals Eat Plant Leaves